Summer Solstice 2023: June 21 is the longest day of the year! Here’s why

Yesterday we witnessed the longest day of the year, and it also marks the beginning of the Summer Solstice. Here’s why.

June 21 is the longest day of the year. (NASA)

During the Earth's trip around the Sun, solstices come around twice a year, at the points in Earth's orbit where this tilt is most pronounced. The summer solstice begins around June 21 whereas the December solstice arrives on December 21. Solstices also mark the change of seasons throughout the year. The first day of the Summer Solstice marks the day when the Sun is directly over the Tropic of Cancer which is located at 23.5° latitude North. June 21 is also the longest day of the year, but why is it so?

The science behind Summer Solstice

Firstly, Solstice means ‘sun stands still' in Latin. According to NASA, solstices and equinoxes serve as indicators of the seasons, resulting from the Earth's axial tilt of 23.5 degrees with respect to its orbital path around the sun. Due to the tilt, different parts of the Earth receive different amounts of sunlight, depending on the time of year. The Northern Hemisphere is tilted toward the sun during Summer Solstice, meaning it receives the full solar glare on these days. Moreover, the farther you go in the Northern Hemisphere, the more hours of sunlight you'll see. Therefore, it makes June 21, which is the beginning of the Summer Solstice, the longest day of the year.

However, the Summer Solstice doesn't always occur on the same day every year. This is because while the Gregorian Calender has 365 days, Earth takes about 365.25 days in reality. That is why one more day is added every four years, which is known as the leap year.

Why is Earth tilted?

NASA states that a long time ago, a massive object called Theia, about the size of Mars, collided with our planet, knocking it off its axis a bit. So instead of rotating straight up and down, Earth leans a bit off its axis. Moreover, this collision also resulted in the formation of the Moon, which is Earth's only natural satellite.